Particle System Instances Retaining Dimensions of Original Object
Particle System properties &gt; Emission &gt; Hair Length 1
Particle System properties &gt; Render &gt; Scale 1


Notes:

If Hair length is set 2, than Render Scale should be 0.5, and so on to keep size equal.
If dimension of source object is not 1 check also if Particle System properties &gt; Render &gt; Object &gt; Object Scale is ON